Downtown Reykjavik on a blustery August morning. Rock, scrubland and the Atlantic Ocean surround the capital of Iceland. This is, by some measures, the fifth wealthiest country in the world, a land of geysers, glaciers, volcanos, fish, and rain. And money. Icelanders are gaining an ever bigger stake in British business, especially on the high street where they already control House of Fraser, H Samuel, Hamleys, Whittard of Chelsea, Oasis, Mappin & Webb, and of course the frozen-food chain Iceland.

At the central offices of Landsbanki, Iceland's oldest bank, Bjorgolfur Gudmundsson sips mineral water in a plush suite. He is chairman of the board and a billionaire. He and son Thor are the major shareholders. Gudmundsson, the world's 799th richest man according to Forbes magazine, has lived a rich life in more ways than one.

The 66-year-old is a former footballer, furniture packer and law student, a recovering alcoholic of 30 years, and an old-fashioned philanthropist. In the 1990s he was sentenced to 12 months in prison, suspended for two years, for bookkeeping offences. He went to Russia, defied the St Petersburg mafia, remade his fortune and returned triumphant to Iceland, where he has interests in shipping, publishing, food, communications and property. These reach throughout Europe and into Asia and the Americas. If you buy seafood from Tesco or Marks & Spencer, the chances are Gudmundsson enjoys a cut of the profit.

And, despite the frequent sightings last season of Eggert Magnusson, with his bald head in despairing hands, it is Gudmundsson who has owned West Ham since last November, not the Elmer Fudd lookalike. 'The club's win against Manchester United at Old Trafford must be my single most joyous moment in football. It was a fantastic finish to an exceptional season,' says Gudmundsson, describing West Ham's escape from relegation on the final day.

Following the takeover, Alan Pardew was sacked and replaced as manager by Alan Curbishley. Tales of gambling on the team coach, unhappy players and dressing-room cliques featured almost daily in newspaper headlines. And West Ham kept losing. There was also the on-going Carlos Tevez affair (see panel below). But in April the club escaped a points deduction for their failings in his controversial signing and, once the Argentine started scoring, the seemingly impossible began to happen.

Following months of negotiation, Observer Sport has been invited to Iceland for Gudmundsson's first interview with a British newspaper. There are nine Premier League clubs with foreign owners. They give few interviews and consequently little is known about the characters who, effectively, control nearly half of the world's richest football league. They can appear a little distant. At Old Trafford on West Ham's great day, Joel, Avram, and Bryan Glazer, the sons of Manchester United owner Malcolm, failed to acknowledge Gudmundsson and his entourage when they sat together in the directors' box. It was only later, as both parties waited at the airport to board private jets, that the wife of one of the brothers offered a greeting.

As well as Glazer, Gudmundsson is joined by Roman Abramovich, who bought Chelsea in 2003; Mohamed Fayed, who has owned Fulham for a decade; and a group of others who have also acquired clubs in the past couple of years: Randy Lerner at Aston Villa, George Gillett and Tom Hicks at Liverpool, Alexandre Gaydamak at Portsmouth, Thaksin Shinawatra at Manchester City and Niall Quinn's Irish consortium at Sunderland.

Why did Gudmundsson buy West Ham? Was it to join this exclusive band and gain the status that comes with owning a club in a league watched and envied around the world? 'Well, the Premier League is considered the mecca of football and it should be treated in that way,' he says. 'So to be able to participate there is something that I never expected, and it is a privilege. Also, I am at the stage of life where I'm fortunate to be able to do whatever I like - I can get more out of this really than earning more money.'

Gudmundsson's impeccable manners, gentle demeanour and boyish humour ensure he holds the attention. 'I have interests in companies all over the world. Our operations in Iceland are minimal. Most of our money comes from abroad.

'And I think I've been involved in most areas of Icelandic culture - a symphony orchestra, young rock stars, I have supported most of them. We have a fund that is assisting young students. West Ham is a very little part of my interests.'

Football, though, is a passion. Last season he attended nearly all of the club's matches at Upton Park and watches about one in three of West Ham's away games, though was not at Reading yesterday. He and his associates also have boxes at Chelsea and Arsenal.

Gudmundsson was a youth-team player at KR, Iceland's most successful club. He was chairman during the 1990s and later on the day we meet watches his grandson, a striker for KR, play. One favourite football memory, he says, is when the club won the championship in 1999 'for the first time in 30 years'.

Magnusson, the chief executive and chairman, has shielded Gudmundsson throughout West Ham's problems. This is why the former biscuit manufacturer is perceived as the owner. 'Yes, Eggert is in the forefront, managing the whole thing, but we can't let him have all the attention. Though anyway, I'm more silent behind him.' Why? 'I'm occupied with all my businesses so we discuss things on the phone. Think of Eggert as the Coca-Cola sign!'

When Observer Sport arrives at the bank, Gudmundsson has asked Magnusson to sit in for a while because: 'I think it's more interesting to listen to both of us. We're in this together. And we're going to make it together. We have very similar views, similar ideas. This is how West Ham came about. We met last year and were discussing life. Eggert told me perhaps he would be leaving Uefa and he was wondering what to take up next. And when West Ham came on the table I thought perhaps it could fit into Eggert's way of thinking. That's how it started.

'It all came through the Landsbanki in London and I was considering this investment opportunity - obviously I had to think how to run it, who would be responsible for the operation. Then I remembered my conversation with Eggert and I called him.' This friendship is also reflected in what appears a productive business relationship. Surviving last season must have helped. 'We just didn't expect the hurdles waiting for us, beginning with Pardew leaving,' Gudmundsson admits.

Following the club's survival, Curbishley allowed Nigel Reo-Coker, Marlon Harewood, Paul Konchesky and Yossi Benayoun to leave. Craig Bellamy, Kieron Dyer, Freddie Ljungberg, Scott Parker and Julien Faubert came in at the cost of £22.1million, though at least £11m has been recouped from sales. 'Now the atmosphere in the dressing room is optimistic because the characters we have are different,' Gudmundsson says. What of the colourful Bellamy? 'Boris Johnson is colourful and he might be soon be running your country's capital,' is his reply.

Does Curbishley choose whom to buy? 'He has to convince, because there's money involved, but of course he is the one that sells us the [idea of signing] a player.'

Some have wondered whether the growing influence of foreign owners is good for the English game. As well as stressing how he and Magnusson 'consider ourselves as semi-English', Gudmundsson disputes the premise of such questions. He uses the case of Dyer, injured during the week at Bristol Rovers and whose transfer was held up after Newcastle United suddenly upped their price. 'There is this worry about foreigners coming into the Premier League and [English people] dealing with them. Well, these were not foreigners at Newcastle. We were dealing with British gentlemen!'

It is said with a twinkle. Gudmundsson can see the humour in most situations. In 1961 he began two years at law school but 'I became interested in business, so decided that perhaps I would be the person to give the jobs to lawyers'.

Gudmundsson is adamant that his commitment to West Ham is long term. Would he go through something like the Tevez saga all again? 'We are very much not speculating at what could have happened. We know what happened. And we are here today and we are preparing for the future. Yesterday is only part of the past. But to do this again? I mean, we are experts on this. Problems, problems - it's just solving them and starting fresh. I would not hesitate to go through it again. No hesitation at all.'

Gudmundsson knows how to fight. Two years ago he pulped thousands of copies of a book due to be published by his own publishing house, Edda, because of a section about his wife. Gudmundsson is married to Thora Hallgrimsson, 11 years his senior, and a member of a widely respected Icelandic family. Her father was head of Shell Iceland; one uncle was an ambassador to the United States in the 1940s, while another the prime minister on five occasions up to 1963. Her former husband, George Lincoln Rockwell, with whom she had four children, founded the American Nazi Party in 1959 before he was assassinated eight years later.

Edda's book on the history of Thora's family, The Thors, contained some pages that offended Gudmundsson, leading to the pulping of the original. The author agreed to a rewritten version with just a single mention of that first marriage. 'This was unfairly done,' Gudmundsson says. 'What they were trying to do was involve my wife and her first husband 50 years ago. I mean, you don't do this to innocent people. This was a book about the family and all of a sudden they were trying to picture, feature her history, as the main thing of the family. It was irrelevant to the whole story.'

As a side effect of this saga, Gudmundsson and Thor, his and Thora's only child, attempted to buy DV, a daily Icelandic tabloid, simply to close it down because of its coverage. One front-page headline read 'The Missing Chapter'. But the public were not impressed by the paper's coverage, underlining Gudmundsson's popularity. 'I'm not interested in controlling things,' he says. 'But we have press in Iceland that is exactly the same as in England. There are people that want to scoop something - I'm used to this as I'm a very public figure.'

Gudmundsson believes he also suffered unjustly over his conviction for five minor book-keeping offences. Many in Iceland believe he and his fellow executives, faced with around 450 charges the overwhelming majority of which failed, were the victims of a political battle between rival shipping companies: Gudmundsson's Hafskip, which he took over in 1979, and Eimskip (which he has now bought). The country's then finance minister was a shareholder and former chairman of Hafskip, which became insolvent in 1985, prompting politicians to call for an investigation. The case dragged on for six years.

After his conviction, Gudmundsson focused on restoring his fortune and the standing of his name. 'The fight was to recover. To regain my strength in business. And money-wise. I was left almost broke, so I think I took the right decision to put emphasis on my family, and to re-establish my status. But this case doesn't ever go away, it doesn't go away.'

Was it politically motivated? 'People say so, but I'm not going to comment on that. I'll say two things. Number one, I'm sure that a case like this could never happen again in Iceland today.' Why? 'Because this society now is so different. Then it was much more closed. Since we became involved in Europe, everything changed.

'Secondly, my feeling is much healthier than the authorities who were dealing with the case. I know I wouldn't change places. I'm not mentioning conscience or anything like that, but inside myself I have nothing to hide and I feel so confident. So if you ask anyone in Iceland, I have regained everything I had before, including respect. But I would say that regarding those involved from the authority side... well, I would never change places with them today.

'In business you prepare for the best and the worst, especially when you have been through all of that. We have seen it all and the main thing is we are stronger than ever.'

In 1991, Gudmundsson and Thor, who became Iceland's first billionaire in 2005 and is ranked more than 500 places higher than his father on Forbes' list, made that move in St Petersburg with partner Magnus Thorsteinsson. There they began Bravo, a soft-drinks company that became a brewery and was eventually bought by Heineken.

This was perhaps an unusual career move for a recovering alcoholic. Gudmundsson's battle with drink moved him to found Iceland's first drug-and-alcohol rehabilitation programme at a time when there was little sympathy for substance-abuse problems. 'I've been doing that for 30 years. We run treatment and family centres - it's a very strong movement here and I'm very happy to do so.'

Of the business venture in Russia, he says: 'We came at the right time and went to the right place. St Petersburg was the city closest to the West, and to Finland, which we knew very well - it was the window during the communist years.'

Asked if he understands Russian, Gudmundsson says: 'Very little. But my son and Magnus can. They were there for 10 years. It was very tough and we never knew if we would go down or up. We did everything right, we did everything right in the end. And we were supported by and had investors from institutions and banks in the West. Heineken is Dutch. This was their entry into the country. So we got paid in Holland or England. But somehow people like to talk about those who have been working in Russia as it being mafia or Russian money. It's no such thing. We delivered one of the best companies. And Heineken have really taken off, are flying higher and higher. They are so grateful they managed to acquire the business.'

Thor has commented about that time: 'People will think twice about messing with you if you are actually a government representative.' This was a reference to his status as honorary consul for Iceland. Gudmundsson has the same role in Bulgaria where, as in the Czech Republic, the family have interests in telecoms. So, were there any threats from the mafia? 'Of course. In every country, if you stay to your principles you can survive there. It's only when you give in that you're in trouble. And I can tell you one thing, that if we had any contact with dubious people Heineken would never have bought the company. They are still so grateful that they managed to acquire the business.'

West Ham seem to mean more to Gudmundsson than the brewery did. 'I am aware of the greatest moments in the club's history over the last 40 years. I know how it's said that West Ham won the World Cup for England in 1966 because of the goals from Martin Peters and Geoff Hurst, and the immense contribution from Bobby Moore. And I have also met Billy Bonds, who was captain when the club won the FA Cup.

'There is also a good response from the local council,' he says of the proposed move to a new stadium at a site half a mile from Upton Park. 'I believe we can become one of the top English clubs, and in Europe, again. We want Champions League football and believe we can win the Premier League in time. Why not? Of course we do not think it will happen tomorrow, it will take some years. But definitely we are heading there. And I think we now have all that's needed for that.'